Everyone has a different argument, but at the end of the day it really should boil down to ROI.
And compared to other investments in the world, 6 months to make all your money back (and potentially a lot more if you hold your BTC), is a pretty good investment if you ask me.
What it really boils down to is $/gh and w/gh and delivery date.
ROI is all speculative but the simple fact is that if the S4's profit the Prismas will profit more.